The disclosed apparatus and method relate with particularity to Ser. No. 844,520 filed on even date herewith, now U.S. Pat. No. 4,197,797 entitled "Modular High Speed Printing System" and assigned to the common assignee. The instant modular article tracking logic system exhibits utility in any modular article processing system wherein it is necessary to monitor the passage of individual articles through a plurality of processing modules. Since the processing system is modular it is highly advantageous that the article tracking logic system be expandable to accommodate the additional processing capability of the processing system as additional processing modules are employed. Similarly, the logic system should have the functional flexibility to accommodate the assembly of processing modules in any order. Also, the logic system should be capable of indentifying both the occurrence and location of processing failures and bring the processing system to a logically consistent halt such that all articles will be accounted for and any article which may be processed will be processed.